An inductor is a component constituting a circuit used in radio frequency (RF) transmission and reception, and is essentially and extensively used in RF semiconductor devices and analog devices which are widely used and gaining in popularity with the expansion of the wireless communication market. Conventional inductor structures in semiconductor devices are typically octagonal structures formed horizontally over a semiconductor substrate surface. Such inductor structures require and consume considerable amounts of substrate area and this represents a major disadvantage in the ongoing effort to reduce feature size, increase miniaturization and increase levels of integration. The inductance value of an inductor is directly related to the radius of the octagonally shaped horizontal inductor and therefore greater inductance values require an inductor that consumes a large amount of substrate area. This area consumption comes at the expense of additional device features for a fixed-size chip or requires a larger size chip to provide the same functionality. Either of these scenarios, i.e., a larger chip size or the need to utilize more chips to produce a component, increases cost to the consumer.
The performance of an inductor is indicated by the quality factor, Q, which is the ratio of energy stored in the inductor to the energy loss in the inductor. More particularly, Q is the ratio of an inductor's inductive reactance to its resistance at a given frequency, and is a measure of the inductor's efficiency.
Conventional inductor structures formed horizontally over a semiconductor substrate surface produce magnetic fields extending into the substrate and oriented such that the primary axis of the generated oblong magnetic field is normal to the substrate surface. There is thus a strong interaction between the magnetic field and the semiconductor substrate. In the presence of a magnetic field, electromagnetic induction results in an induced electromagnetic force, emf, which produces local currents in the conducting core normal to the magnetic flux. These currents are called eddy currents and the eddy currents are undesirably formed in the semiconductor substrate due to the location of the magnetic field and undesirably propagate through the semiconductor substrate. This results in power loss at high frequencies. Moreover, the performance of the inductor is degraded and difficult to predict as a result of complicated substrate effects when eddy currents propagate through the semiconductor substrate in high frequency devices.
It would therefore be desirable to provide an inductor structure that is efficient, includes a high Q factor, requires minimal substrate surface area and does not suffer from the above shortcomings and limitations.